This invention relates to electrically programmable fuses, and particularly to an electrically programmable fuse having an interrupted silicide layer and a fabrication method, which creates controlled electromigration flux divergence during a programming operation of the fuse.
Electrically programmable fuses have been employed in many advanced technologies within the semiconductor industry. These fuses are utilized for various integrated circuit applications such as an implementation of array redundancy, field programmable arrays, and chip-ID trimming circuits. These fuses may be programmed to store data on an integrated circuit, to adjust components on the circuit or to program logic on the circuit, for example. During programming of a conventional electrically programmable fuse, electromigration of silicide results in a local depletion or void of silicide on top of a polysilicon layer at a flux divergence region (i.e., near a junction region where out-flowing flux is greater than in-flowing flux) and in a high resistance. Flux divergence may be induced in various ways such as microstructure (e.g., grain-boundary) variation, configurational variation, or by temperature gradient. FIGS. 1A through 1C illustrate a conventional electrically programmable fuse before, during and after programming of the fuse, respectively. FIG. 1A shows an electrically programmable fuse 10 which includes an anode 16, a cathode 18 and a fuse link 20. The anode 16, the cathode 18 and the fuse link 20 include a polysilicon layer 12 (as shown in FIG. 1C, for example) which is a high resistance material and a silicide layer 14 which is a low resistance material formed on the polysilicon layer 12. A plurality of contacts 22 are formed on the anode 16 and cathode 18, respectively. The conventional electrically programmable fuse 10 is designed such that a width difference between the fuse link 20 and the cathode 18 results in current density variation. As shown in FIG. 1B, during programming, higher temperature (as indicated by the large arrow) results in temperature gradient, and a large reservoir of silicide occurs on the cathode 18 (as indicated by the small arrows). As a result, as shown in FIG. 1C, several problems occur when programming the conventional electrically programmable fuse 10. For example, massive damage in the silicide layer 14 occurs at a cathode junction where the cathode 18 and the fuse link 20 meet, thereby creating an extended silicide depletion region 24 extending into the cathode 18. Further, the fuse link 20 requires high energy (e.g., high current) to program which may have a thermal or mechanical impact, or cause damage to the contacts 22, for example.